Module 105 Criticality Safety

DOE-HDBK-1113-98

Module 105 Criticality Safety

Lesson Plan

Instructor's Notes

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MODULE 105 - Criticality Safety

Objectives

NOTE: The training material in

EO8

Describe the criticality safety control measures for

this module is not a substitute

uranium, including inventory control measures.

for criticality safety training.

EO9

Identify criticality monitoring techniques used with

uranium.

Explanation of Criticality

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Energy given off during fission

Uranium is a fissionable material, which means that it can

is approximately 200 MeV.

undergo nuclear fission. Nuclear fission is a process in

which a very heavy unstable atom primarily splits in two, or

"fissions". When an atom fissions, one large atom

primarily becomes two smaller atoms, between one and

seven neutrons are given off, and a great deal of energy in

radiation and other forms, such as the kinetic energy of the

fission fragments, is released.

Some unstable atoms, such as 235U, undergo a small amount

of fission without any outside influences. This small

amount of spontaneous fission does not present a

significant hazard on its own, but the neutrons from this

fission may be absorbed by other fissionable atoms. When

an atom of fissionable material absorbs a neutron, the

already unstable atom gains additional energy and becomes

even more unstable. One way the unstable atom can get rid

of its excess energy is through fission.